The present invention relates to a drug comprising a modified N-acyloxylated cycloalkyl compound as an effective ingredient and, more particularly, to a drug comprising an N-acyloxylated cycloalkyl compound which can scavenge in vivo active oxygen or free radicals and is useful as an agent for preventing or curing various diseases induced by in vivo active oxygen or free radicals and as a reagent for non-invasively acquiring biological images by a magnetic resonance method, typified by the ESR (Electron Spin Resonance) method, or for detecting in vivo active oxygen or free radicals in collected organisms.
Active oxygen is defined as one type of oxygen species with a short life which is very reactive and takes part in various types of in vivo oxidation reactions. The scope of active oxygen varies depending on the definition. In a narrow sense, active oxygen means a hydroxyl radical (.OH), superoxide (O2xe2x88x92), singlet oxygen (1O2), and hydrogen peroxide (H2O2). In a broad sense, active oxygen includes a peroxy radical (LOO.) and alkoxy radical (LO.) which are derived from the reaction of the above active species and biological components such as unsaturated fatty acid L, and a hypochlorite ion (ClOxe2x88x92) formed from H2O2 and Clxe2x88x92 by the reaction with myeloperoxidase and the like.
Radicals are defined as atoms or molecules which possess one or more unpaired electrons. A hydroxyl radical, superoxide, peroxy radical, and alkoxy radical are all radicals. Singlet oxygen and hydrogen peroxide are not radicals, but are formed from a radical reaction or cause other radical reactions.
In recent years, active oxygen and free radicals showing various in vivo bioactivity have attracted attention and have been studied in the field of biology, medicine, and pharmacology. The active oxygen or free radicals are generated in vivo due to ultraviolet rays, radiation, atmospheric pollution, oxygen, metal ions, ischemia-reperfusion, and the like. Active oxygen and free radicals thus generated cause various in vivo reactions such as peroxidization of lipids, denaturation of proteins, and decomposition of nucleic acids. Ischemic diseases, digestive diseases, cancer, cranial nervous diseases accompanied by nerve degeneration, inflammation, cataracts, and drug-induced organopathy are known as diseases accompanied by such phenomena. Noninvasive detection of such active oxygen and free radicals which relate to so many diseases may help in the investigation of the causes of a number of such diseases and provide useful medical information.
The following two methods are known as conventional methods for detecting free radicals. One of these is an indirect method consisting of adding a reagent to a reaction system and detecting the resulting changes in absorbance or emission of light by the reaction system. The other method is an electron spin resonance (ESR) method consisting of directly detecting unpaired electron of free radicals. Since the ESR method can measure both liquid and solid samples and even opaque or non-uniform samples, this method is very advantageous for detecting active oxygen in collected biological samples or in vivo.
The problem in detecting in vivo active oxygen or free radicals is that ESR cannot directly measure active oxygen or free radicals in a living body due to their short life. To solve this problem, a method of indirectly observing in vivo active oxygen or free radicals by administering a reagent to a living body and measuring the chemical changes in the reagent caused by active oxygen or free radicals using ESR has been employed. For this purpose, a spin trapping method has been developed with an objective of measuring active oxygen having unpaired electrons such as hydroxyl radicals. This method makes use of the capability of a trapping agent to rapidly react with free radicals having only a short life and produce a spin adduct which is stable, has a long life, and can be detected by ESR, as shown in the following formula. In a narrow sense, the spin trapping agent has been defined as a compound having a double bond in the scavenging site, such as 5,5-dimethyl-1-pyrroline-1-oxide (DMPO) shown below. 
Specifically, measurement of short-life active oxygen becomes possible by adding a compound which can rapidly react with radicals and produces a spin adduct sufficiently stable for measuring ESR to the measuring system as a spin trapping agent, and measuring the stable spin adduct.
Therefore, the requirements to be satisfied by the compound used as a spin trapping agent include: (1) capability of rapidly reacting with active oxygen and free radicals, (2) being converted into sufficiently stable radicals, (3) being chemically stable when handled, and (4) being free from toxicity.
An attempt to directly detect or image in vivo active oxygen or free radicals by using the above spin trapping agent has been undertaken. However, large volume biological samples cannot be measured using conventional ESR devices which utilize microwaves of an X-band (about 9.5 GHz) due to high dielectric loss in water.
In recent years, ESR-CT utilizing low-frequency microwaves (300-2000 MHz) has been developed, making it possible to directly detect or image free radicals in a sample containing a large amount of water, particularly, free radicals in a living body.
The principle of a nuclear magnetic resonance (NMR) method was discovered in 1945. In 1973, Lauterbur first applied the NMR method to magnetic resonance imaging (MRI) which is an imaging device used in medicine. Since then, the NMR method has progressed remarkably and becomes one of the most universal diagnostic methods at present.
MRI first appeared as a diagnostic method using no contrast media. At present, contrast media are used to increase the detectability of a lesion site which is difficult to shade. Therefore, contrast media exhibiting superior detectability are demanded.
In recent years, the utility of nitroxide compounds as contrast media for MRI or ESR and the antioxidation effect thereof has attracted attention. For example, paramagnetic inorganic compounds such as gadolinium are administered as contrast media to contrast the lesion site in the MRI diagnosis used in medicine. However, because of toxicity of such inorganic compounds, nitroxide compounds have been considered as MRI contrast media which can be used instead of gadolinium. As ESR imaging has been developed and the utility thereof has attracted attention, the utility value of nitroxide compounds as imaging agents has increased. The possibility of utilization of nitroxide compounds as an active oxygen scavenging agent has also been suggested (see J. Biol. Chem. 263: 17921; 1998).
If information about active oxygen or free radicals in biological tissue can be acquired as biological images by the noninvasive magnetic resonance measuring method, this information can be used for studying pathology in which active oxygen and free radicals take part, such as ischemic diseases, digestive diseases, cancer, cranial nervous diseases accompanied by nerve degeneration, inflammation, cataracts, and drug-induced organopathy (hereinafter referred to xe2x80x9cdiseases related to active oxygen and the likexe2x80x9d) and diagnosing these diseases.
In this situation, a report has been published describing the characteristics of some type of hydroxylamine derivative which can easily react with free radicals and active oxygen by oxidative stimulation (active oxygen, etc.) and be converted into a nitroxide compound having ESR signals (Biochem Biophys Res Commun 230, 54-57, 1997). The compound is not a spin trapping agent in the stringent sense because this is not a generally defined nitron or nitroso compound. However, inasmuch as the capability of scavenging spins as shown by the following formula, the compound has the same function as the spin trapping agent in a narrow sense. 
In the above formula, Axe2x80x2 represents an alkylene group which may be substituted.
Although it has been known that super oxide in solutions or cells can be detected by measuring the ESR signals of the nitroxide compound formed by the above reaction, the hydroxylamine derivatives presented a serious problem in applying the above reaction to the detection of active oxygen and free radicals. Specifically, although nitroxide compounds derived from hydroxylamine derivatives are such stable compounds that these compounds can be stored for several weeks in an aqueous solution and crystals thereof can be stored for several years in a desiccator (see, for example, Arch. Biochem. Biophys. 215: 367-378; 1982), the hydroxylamine derivatives themselves are unstable and must be prepared each time they are used.
For this reason, although a certain hydroxylamine derivative has been used for the detection of free radicals or active oxygen in solutions or cells, there have been no examples of acquiring images of free radicals and active oxygen generated in the organs by in vivo administration of a hydroxylamine derivative. The reason why this image acquisition has not been successful is considered to be because the in vivo reaction of the hydroxylamine derivative and free radicals is so fast that the hydroxylamine derivative is metabolized in blood before reaching the organs.
Therefore, development of a technology using a hydroxyamine derivative, which functions as a spin trapping agent and can rapidly react with free radicals or active oxygen in an objective organ and yet exhibit excellent stability during preparation or administration, has been desired.
In order to solve the above problems, the inventors of the present invention have conducted extensive studies to discover a compound which is itself stable, rapidly reacts with active oxygen and free radicals in living bodies producing stable products, and possesses guaranteed safety in living bodies. As a result, the inventors have found that an N-acyloxy cycloalkyl compound obtained by acylating the hydroxyl group of a certain hydroxylamine derivative satisfies the above requirements, can scavenge free radicals and active oxygen, and can be effectively used for the detection or deletion of such free radicals and active oxygen.
Acquiring images of free radicals and active oxygen by spin trapping has conventionally been considered to be difficult. However, since the above N-acyloxylated cycloalkyl compound is a compound produced by stabilizing a hydroxylamine derivative having the same function as a spin trapping agent, this compound is stable after preparation and can be transferred to the target organs without being metabolized after administration. The compound is then hydrolyzed into the hydroxylamine derivative, which reacts with active oxygen or free radicals in the organ to produce a nitroxide emitting ESR signals. The inventors have found that images of active oxygen or free radicals can be acquired by detecting the ESR signals.
The inventors have further found that the N-acyloxylated cycloalkyl compound can scavenge active oxygen and free radicals, and can be used as a preventive or therapeutic agent for diseases such as ischemic diseases, digestive diseases, cancer, cranial nervous diseases accompanied by nerve degeneration, inflammation, cataracts, or drug-induced organopathy, as a drug such as an image diagnosis agent or a detection reagent, and the like.
Accordingly an object of the present invention is to provide a drug or reagent containing an N-acyloxylated cycloalkyl compound shown by the following formula (1) as an effective ingredient, 
wherein A represents a C4 or C5 alkylene group which may have one double bond in the ring and may be substituted with an alkyl group, amino group, amide group, carbamoyl group, carboxyl group, keto group, hydroxyl group, sulfonic acid group, phenyl group, acetoxyl group, or acetoamino group, and R is a C1-C3 alkyl group or phenyl group.
Another object of the present invention is to provide a method of scavenging in vivo active oxygen or free radicals comprising administering the above N-acyloxylated cycloalkyl compound (I).
Still another object of the present invention is to provide a novel N-acyloxylated cycloalkyl compound represented by the following formula (IIxe2x80x2), 
wherein m is 0 or 1; when m is 0, Xxe2x80x2 and Yxe2x80x2 individually represent a hydrogen atom, alkyl group, amino group, amide group, carbamoyl group, carboxyl group, keto group, hydroxyl group, sulfonic acid group, phenyl group, acetoxyl group, or acetoamino group, and when m is 1, Xxe2x80x2 and Yxe2x80x2 individually represent a hydrogen atom, alkyl group, amino group, amide group, carbamoyl group, carboxyl group, keto group, hydroxyl group, sulfonic acid group, phenyl group, or acetoamino group; R is a C1-C3 alkyl group or a phenyl group; R1, R2, R3, and R4 individually represent a C1-C4 alkyl group; and 
represents a single bond or double bond.